The present invention relates to a three-phase separator for separating off from a fluid gas and particles contained therein, comprising at least one pair of two gas collection caps extending in a horizontal longitudinal direction and each having a plate section, wherein the plate sections converge in the downwards direction and at the bottom ends of the plate sections leave at least one passage, elongated in the longitudinal direction, for the fluid and particles, which passage connects a reactor chamber below the plate sections to a settling chamber above the plate sections, and wherein a discharge opening for fluid, opening into the settling chamber, is provided at a level higher than said at least one passage.
A three-phase separator of this type is generally known. Inter alia, EP-A 244 029 and EP-A 949 463 may be mentioned. Three-phase separators of this type are widely used in installations for the biological purification of water. Such installations comprise a reactor in which a layer of bacterial flocs is provided. Feed means for the water to be purified open into the layer of bacterial floes and above the layer of bacterial flocs means are provided for allowing particles to settle, in particular bacterial flocs, and discharging purified water. The principle according to which such known installations operate is that effluent is fed into a reactor from the bottom and that this water streams upwards through a layer of bacterial floes, dissolved organic pollutants which come into contact with the bacteria being converted into methane and carbon dioxide. The gas produced in this way gives rise to turbulence, as a result of which bacterial floes swirl upwards. The liberated gas is collected below the gas caps of the three-phase separator in order then to be discharged. Settling of the bacterial floes initially entrained by the gas then takes place above the gas caps. These bacterial floes then fall back into the reactor chamber and purified water remains above the cap, which water is discharged.
When the fluid and bacterial floes pass between the gas collection caps a certain acceleration of the fluid takes place, as a result of which it becomes difficult, if not impossible, for the bacterial floes to settle back into the reactor chamber against that flow. In order to counteract this, the gas caps are usually positioned as far apart as possible; after all, a large gap reduces the said fluid acceleration. The disadvantage of placing the gas caps as far apart as possible is, in turn, that the gas bubbles are then also able to escape between the gas caps, which again causes the fluid velocity to increase and, moreover, also leads to inadequate capture of gas bubbles. In order to counteract this, several layers of gas caps are installed, the gas caps in an upper layer overlapping the gap between gas caps in a layer below. The various aspects result in constructions that contain a relatively large number of components and take up a relatively large amount of space.
The aim of the present invention is to provide an improved three-phase separator, which is of a simplified construction and which can be implemented with relatively little structural material.
The abovementioned aim is achieved with a three-phase separator of the type indicated in the preamble,
in that said at least one passage comprises an inlet passage for the fluid containing the particles to be separated off, as well as an outlet passage for particles which have settled in the settling chamber;
in that the inlet passage and the outlet passage are in the extension of one another, viewed in the longitudinal direction; and
in that the discharge opening, viewed in the longitudinal direction and from the inlet passage, is provided level with the outlet passage or beyond the outlet passage.
In the case of the three-phase separator according to the invention the fluid stream containing particles is forced to move horizontally after passage between two gas collection caps, in particular passage between the plate sections thereof. The reason for this horizontal movement is that the discharge opening has been displaced in the horizontal direction, i.e. the longitudinal direction, with respect to the inlet passage. During this movement the fluid velocity decreases as a consequence of the space through which the fluid has to flow, i.e. the settling chamber, becoming wider. As a consequence of the lower fluid velocity, the bacterial flocs settle and, after some horizontal displacement, pass through the outlet passage back into the reactor chamber located below the caps.
According to the invention it is advantageous if the surface area of the inlet passage is greater than the surface area of the outlet passage. When the surface area of the inlet passage is chosen to be greater than the surface area of the outlet passage, the inlet passage will offer lower resistance than the outlet passage to the upward fluid stream, as a consequence of which the rising fluid stream will automatically select the inlet passage as inlet, so that the outlet passage is able to allow the settled sludge to fall back into the reactor chamber via the outlet passage of smaller surface area.
According to an advantageous embodiment of the invention the surface area of the inlet passage is at least 30%, preferably at least 60%, such as, for example, approximately 70%, greater than the surface area of the outlet passage. It has been found that with a difference of approximately 25% in the magnitude of the surface area although the three-phase separator does not function in the optimum manner it does function reasonably and that the separation capacity with regard to the entrained particles is good from a difference in width of 50% and that, in particular, very good results can be achieved with a difference in width of approximately 70%.
In order further to minimize the risk of incorrect fluid flow through the outlet passage, it is preferable according to the invention if the surface area of the inlet passage is at most 5xc3x97, preferably at most 3xc3x97, as large as the surface area of the outlet passage. In this way it is ensured that the outlet passage is sufficiently large to allow passage of the stream of separated particles, often also with some fluid as well in which the particles, as it were, can still float.
According to a further advantageous embodiment of the invention, viewed with respect to a first vertical touching a first bottom edge part of the one plate section, at the location of the inlet passage, the other plate section extends underneath said first bottom edge part to beyond said first vertical. In this way the underside of the inlet passage is screened by a continued projecting part of a plate section, so that rising gas bubbles are prevented from passing through the inlet passage, or at least it is made more difficult for them to do so. For the same reason it is advantageous if, viewed with respect to a second vertical touching a second bottom edge part of the other plate section, at the location of the outlet passage, the one plate section extends underneath said second bottom edge part to beyond said second vertical. The screening of the outlet passage by means of a section of a plate section continued beneath it, in combination with the screening of the inlet passage from the underside by means of a section of the other plate section continued beneath it, has the advantage that what is achieved at the same time is that the inlet passage and the outlet passage open in different directions (with respect to a vertical) and that it is thus made more difficult for particles flowing back into the reactor chamber via the outlet passage to be immediately entrained again so as to return to the settling chamber through the inlet passage.
According to a further advantageous embodiment of the invention, the settling chamber is provided with a ceiling that closes off this settling chamber from above and that at the longitudinal edges on either side adjoins the respective caps and the discharge opening is provided in the ceiling and, preferably, the top of the discharge opening is covered by a discharge cap with an outflow opening opening in the horizontal direction. This embodiment is particularly advantageous when an aerobic reactor is placed on top of an anaerobic reactor, which aerobic and anaerobic reactors are then separated from one another by the three-phase separator.
According to a further aspect, the present invention relates to an installation for biological purification of effluent, comprising a three-phase separator according to the invention, wherein a layer of particles in the form of bacterial floes, such as sludge or granules, is present in the bottom of the reactor chamber and wherein a feed for the effluent to be purified opens into or below said layer. With the installation according to the invention it is particularly advantageous if the discharge opening is in communication with a further reactor chamber of, in particular, a biological reactor.